Self-locking plug

ABSTRACT

A compact, highly-reusable, self-locking includes a body component, a flexible beam finger component with a plurality of axially-oriented flexible beam fingers, a tab sleeve component including one or more downward extending tabs, an annular detent ring component including a plurality of detents in radial alignment with the plurality of flexible beam fingers, and a wave spring disposed between the tab sleeve component and the annular detent ring component for providing a biasing force to urge the tab sleeve component in a direction of a central, longitudinal axis of the self-locking plug. The flexible beam finger component moves relative to the annular detent ring component when the body component is rotated about the central, longitudinal axis, A, of the self-locking plug, thereby causing the plurality of flexible beam fingers to travel across the plurality of detents and cause elastic deformation of the flexible beam fingers.

BACKGROUND OF THE INVENTION

The invention pertains to plugs, and in particular to a self-locking threaded plug that can be used as a borescope plug, a drain plug, an access plug, a chip detector plug, and other similar threaded parts.

In the aircraft engine industry, for example, many engines include double walled structures, such as a compressor, a combustor and the like, where the outer and inner walls are respectively provided with a number of borescope holes or ports. One purpose of the borescope ports is to allow inspection and monitoring of the engine. This may be accomplished by inserting inspection equipment, such as borescopes and/or probes, through the borescope ports.

Each borescope port requires a removable borescope plug to facilitate borescope inspection of the engine components through the borescope port. In addition, the borescope plug also performs a sealing function to prevent the leakage of high pressure and high temperature gas through the borescope port. Typically, the borescope ports are threaded holes in the engine cases and the borescope plugs typically screw into the ports. The borescope plugs are required to incorporate a secondary locking feature to prevent them from loosening and/or falling out while the engine is operation.

The secondary locking feature can include a number of different schemes. For example, safety wire (lock wire), tab washers, and cotter clips have been used in early engine designs. As the engine designs matured, it became obvious that self-locking secondary locking features provided improved reliability and maintainability. Many new engine designs specify self-locking borescope plugs.

Thus, there is a need to provide a self-locking plug that is highly reusable, robust in function, not prone to damage, does not contain sharp edges, does not have loose parts, and does not require special tools, techniques, or knowledge to operate. Additionally, the self-locking plug should be compact, lightweight, and easy to manufacture.

SUMMARY OF THE INVENTION

In one aspect, a self-locking plug comprises a body component; a flexible beam finger component disposed about the body component and including a plurality of axially-oriented flexible beam fingers, each finger having a beveled fingertip; a tab sleeve component disposed within the flexible beam finger component and including one or more downward extending tabs; an annular detent ring component including a plurality of detents separated by ridges in radial alignment with the plurality of flexible beam fingers; and a wave spring disposed between the tab sleeve component and the annular detent ring component for providing a biasing force to urge the tab sleeve component in a direction of a central, longitudinal axis of the self-locking plug, wherein the plurality of flexible beam fingers travel across the plurality of detents to cause elastic deformation of the flexible beam fingers when the body component is rotated about the central axis of the self-locking plug.

In another aspect, a self-locking plug comprises a body component; a flexible beam finger component disposed about the body component and including a plurality of axially-oriented flexible beam fingers, each finger having a beveled fingertip; a tab sleeve component disposed within the flexible beam finger component and including one or more downward extending tabs; an annular detent ring component including a plurality of detents separated by ridges in radial alignment with the plurality of flexible beam fingers; and a wave spring disposed between the tab sleeve component and the annular detent ring component for providing a biasing force to urge the tab sleeve component in a direction of a central, longitudinal axis of the self-locking plug, wherein the flexible beam finger component moves relative to the annular detent ring component when the body component is rotated about the central, longitudinal axis, A, of the self-locking plug, thereby causing the plurality of flexible beam fingers to travel across the plurality of detents and cause elastic deformation of the flexible beam fingers.

BRIEF DESCRIPTION OF THE DRAWINGS

While various embodiments of the invention are illustrated, the particular embodiments shown should not be construed to limit the claims. It is anticipated that various changes and modifications may be made without departing from the scope of this invention.

FIG. 1 is an exploded view of a self-locking plug according to an embodiment of the invention;

FIG. 2 is a cross-sectional view of the self-locking plug of FIG. 1 when assembled;

FIG. 3 is another cross-sectional view of the self-locking plug of FIG. 1 when assembled;

FIG. 4 is an isometric view of the body component according to an embodiment of the invention;

FIG. 5 is an isometric view of the flexible beam finger component according to an embodiment of the invention;

FIG. 6 is an isometric view of the tab sleeve component according to an embodiment of the invention; and

FIG. 7 is an isometric view of the annular detent ring component according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIGS. 1-3, a self-locking plug 10 is shown according to an embodiment of the invention. In the illustrated embodiment, the self-locking plug 10 is intended for use with a borescope port 100, such as the type used in a jet aircraft engine. However, it will be appreciated that the invention is not limited by the intended use as a borescope plug, and that the invention can be used in other applications, such as a drain plug, an access plug, a chip detector, and other similar parts.

In general, the self-locking plug 10 comprises five (5) basic components: a body component 12, a flexible beam finger component 14, a tab sleeve component 16, a biasing component 18, such as a wave spring, and the like, and an annular detent ring component 20.

Referring now to FIGS. 1 and 4, the body component 12 includes a head 22 to allow a tool (not shown), such as a wrench, and the like, to rotate the body component 12 about a central axis, A, of the self-locking plug 10. The head 22 is an internal drive 24, such as a standard square recess, Allen socket, splined socket, an external hex, and the like. The body 22 also includes a flange 26 that engages the annular flexible beam finger component 14 and the borescope port 100 when the self-locking plug 10 is assembled, as shown in FIGS. 2 and 3. Referring back to FIGS. 1 and 4, the body 22 also includes an upper cylindrical portion 28 and a lower cylindrical portion 30 located on the opposite side of the flange 26 than the head 22. As shown in FIGS. 2 and 3, the upper cylindrical portion 28 has an outer diameter, D1, than is slightly smaller than the inner diameter of the borescope port 100, while the lower cylindrical portion 30 has a smaller outer diameter, D2, than the upper cylindrical portion 28. As a result, the lower cylindrical portion 30 can be easily inserted into a central aperture 106 of the borescope port 100 until the flange 26 of the body component 12 engages the borescope port 100. The body component 12 may also include a circular-shaped recess 32 formed in the upper and lower cylindrical portions 28, 30. The recess 32 causes the upper and lower cylindrical portions 28, 30 to be annular in shape, rather than solid, thereby reducing the overall weight of the self-locking plug 10.

Referring now to FIGS. 1 and 5, the flexible beam finger component 14 includes a plurality of flexible beam fingers 34 forming a plurality of slots 35 therebetween. The flexible beam fingers 34 extend upwardly (i.e. in the axial direction or Z-axis direction) in a circular arrangement from a ring portion 36. Each flexible beam finger 34 has a radially inward beveled fingertip 38 adapted to engage the annular detent ring 20. Each beveled fingertip 38 is formed with a pair of opposing beveled side surfaces 38 a, 38 b, a substantially planar side surface 38 c extending between the beveled side surfaces 38 a, 38 b, and a substantially planar top surface 38 d connecting the side surfaces 38 a, 38 b, 38 c. The beveled shape of the side surfaces 38 a, 38 b facilitate the mechanical interaction with the annular detent ring 20. The flexible beam finger component 14 also includes a flange 40 extending radially inward with respect to the ring portion 36. The flange 40 engages the flange 26 of the body component 12 when the self-locking plug 10 is assembled, as shown in FIG. 3.

In the illustrated embodiment, one or more slots 42 are formed in the flange 40. The slots 42 are adapted to receive a corresponding tab 48 of the tab sleeve component 16 when the self-locking plug 10 is assembled, as shown in FIG. 2. In the illustrated embodiment, the flexible beam finger component 14 includes two slots 42 that are arranged to be diametrically opposite each other, i.e., 180 degrees apart from each other. However, the invention is not limited by the number of slots 42, and that the invention can be practiced with any desirable number of slots, so long as the number of slots correspond to the number of tabs formed on the tab sleeve component 16. For example, the flange 40 can have three slots 42 located 120 degrees apart from each other. In another example, the flange 40 can have four slots 42 located 90 degrees apart from each other.

The purpose of the one or more slots 42 is to accommodate the one or more tabs 48 of the tab sleeve component 16 and prevent rotation therebetween when the one or more tabs 48 are received by the one or more slots 42. Thus, the slot 42, in combination with the tab 48, provides an anti-rotation feature between the flexible beam finger component 14 and the tab sleeve component 16 of the self-locking plug 10. It will be appreciated that the invention is not limited by the use of a slot on the tab sleeve component 16, and that the invention can be practiced with other known means for the slot 42. For example, the slot 42 can be replaced with a female hex, a Double-D, or a number of other forms that could be complimentary to the form on the flexible beam finger component 14.

Referring now to FIGS. 1 and 6, the tab sleeve component 16 comprises a generally annular ring 44 and an upwardly extending band 46 having an inside diameter slightly larger than the outside diameter of the head 22 of the body component 12. As a result, the tab sleeve component 16 can be slipped over the head 22 of the body component 12 such that the flange 44 of the tab sleeve component 16 engages the flange 40 of the flexible beam finger component 14 when the self-locking plug 10 is assembled, as shown in FIGS. 2 and 3. The tab sleeve component 16 also includes one or more tabs 48 extending downward from the ring 44. The tabs 48 are adapted to be received by a corresponding slot 42 of the flexible beam finger component 14 when the self-locking plug 10 is assembled, as shown in FIG. 2.

In the illustrated embodiment, the tab sleeve component 16 includes two tabs 48 that are arranged to be diametrically opposite each other, i.e., 180 degrees apart from each other. However, the invention is not limited by the number of tabs 48, and that the invention can be practiced with any desirable number of tabs, so long as the number of tabs correspond to the number of slots formed on the flexible beam finger component 14. For example, the tab sleeve component 16 can have three tabs 48 located 120 degrees apart from each other. In another example, the tab sleeve component 16 can have four tabs 48 located 90 degrees apart from each other.

The purpose of the one or more tabs 48 is to engage a slot 102 formed in the top surface 104 of the borescope port 100 and prevent rotation of the self-locking plug 10 when the head 22 of the body component 12 is rotated by the tool. Thus, the tab 48, in combination with the slot 102, provides an anti-rotation feature between the tab sleeve component 16 of the self-locking plug 10 and the borescope port 100. It will be appreciated that the invention is not limited by the use of a slot on the borescope port 100, and that the invention can be practiced with other known means for the slot 102. For example, the slot 102 can be replaced with a female hex, a Double-D, or a number of other forms that could be complimentary to the form on the borescope port 100. In another example, the slot 102 can be eliminated with a port larger in diameter and holes can be used instead of cutouts. In this example, the tab 48 may have a narrower width to enable the tab 48 to fit into the holes. In yet another example, the port does not include holes or cutouts. Instead, the tab 48 would have a wider width, angled and have a slot machined in the center of the tab 48.

Referring now to FIGS. 1 and 7, the annular detent ring component 20 includes an upper flange portion 50 and a plurality of detents 52 formed on an outer circumferential surface 54. The annular detent ring component 20 has an inner diameter slightly larger than the outer diameter of the head 22 of the body component 12. As a result, the annular detent ring component 20 can be slipped over the head 22 of the body component 12 when the self-locking plug 10 is assembled, as shown in FIGS. 2 and 3. The upper flange portion 50 prevents unwanted axial movement of the flexible beam finger component 14 when the self-locking plug 10 is assembled, thereby acting as a stop. As shown in FIG. 7, each detent 52 has a generally concave surface and is separated by a substantially planar surface 56. The concave profile of each detent 52 facilitates the interaction with the flexible beam fingers 34 of the beam finger component 14.

In the illustrated embodiment, the annular detent ring component 20 includes a different number of detents 52 and beam fingers 34. However, it will be appreciated that the invention can be practiced with any desirable number of detents 52 and beam fingers 34. For example, the invention can be practiced with the same number of detents 52 and beam fingers 34.

To assemble the self-locking plug 10, the flexible beam finger component 14 is disposed about the body component 12. Specifically, the flange 26 of the body component 12 and the flange 40 of the flexible beam finger component 14 engage each other when the flexible beam finger component 14 is disposed about the body component 12. Then, the tab sleeve component 16 is disposed within the flexible beam finger component 14. Then, the wave spring 18 is disposed about the tab sleeve component 16. Finally, the annular detent ring component 20 is fixedly attached to the body component 12 such that the plurality of detents 52 are engaged with the plurality of flexible beam fingers 34.

When assembled, the wave spring 18 is disposed between the tab sleeve component 16 and the annular detent ring component 20. Once the detent ring component 20 is attached to the upper portion 22 of the body component 12, the wave spring 18 provides a biasing force to urge the tab sleeve component 16 in a downward direction (i.e. toward the borescope port 100) along the central, longitudinal axis, A, of the self-locking plug 10. It is noted that the self-locking plug 10 uses the wave spring 18 as a biasing means, rather than a coil spring. It has been found that the use of the wave spring 18 produces less stress than a comparable coil spring, making the wave spring 18 far more resistant to failure by breakage or relaxation as compared to the coil spring. However, it will be appreciated that the invention is not limited by the use of a wave spring to provide the biasing force against the various components, and that the invention can be used with any desirable means that is well-known in the art for providing a biasing force against the various components. For example, it might be advantageous to use a coil spring instead of a wave spring, particularly if there is not a size constraint to do so.

In operation, the flexible beam finger component 14 is free to rotate about the central axis, A, while the annular detent ring component 20 does not rotate once fixedly attached to the body component 12. As the body component 12 is rotated by the tool (not shown) about the central axis A of the self-locking plug 10, the plurality of axially-oriented flexible beam fingers 34 on the flexible beam finger component 14 engage the circumferentially-arranged detents 54 formed on the annular detent ring component 20. As the plurality of detents 54 travel across and engage the flexible beam fingers 34, the detents 54 cause elastic deformation of the flexible beam fingers 34. In other words, the detents 54 cause the flexible beam fingers 34 to be periodically deflected in a radial direction (i.e. in the X-axis direction) by a varying amount, resulting in a biased resistance each time a beam finger 34 (or set of fingers) is deflected. This biased resistance has a positive clicking effect that can be audibly detected by the user, and generates a predictable and measurable prevailing torque, which is precisely engineered to be within a specific range (in lb/in) for a specific number of cycles. This prevailing torque has been shown to prevent loosening of the self-locking plug 10, particularly in aircraft borescope plug applications.

It is noted that the detents 54 are always engaged with the flexible beam fingers 34 when the flexible beam finger component 14 is rotated relative to the annular detent ring component 20. It is also noted that the flexible beam finger component 14 is free to rotate about the central axis, A, but is captured in the axial direction (i.e. in the Z-axis direction) by the annular detent ring component 20 and the borescope port 100, as shown in FIG. 3. Further, the tab sleeve component 16 can move in the axial direction (i.e. in the Z-axis direction), but only by a pre-determined amount, and is eventually captured when the tabs 48 of the tab sleeve component 16 are seated in the slot 102 on the top surface 104 of the borescope port 100, as shown in FIG. 2. It is noted that the biasing force exerted by the wave spring 18 ensures that the tabs 48 remain seated in the slot 102 as the body component 12 is further rotated by the tool (not shown). Once the tabs 48 engage the slot 102, the flexible beam fingers 34 and detents 54 activate and generate prevailing torque as the body component 12 is further rotated further by the tool.

As described above, the flexible beam finger component 14 rotates relative to the annular detent ring component 20. However, it should be appreciated by one skilled in the art that the invention can be practiced in reverse, i.e., with the annular detent ring component 20 rotating relative to the flexible beam finger component 14.

The design of the self-locking plug 10 of the invention has several distinct advantages as compared to conventional plugs. First, the body component 12 of the self-locking plug 10 seats directly against the borescope port 100, which assures superior squareness, strength and sealing. Second, the flexible beam fingers 34 and detents 54 work fully independently of the wave spring 18. As a result, the self-locking plug 10 remains securely seated against the borescope port 100, even though the wave spring 18 may have failed. Third, the use of the wave spring 18, rather than a coil spring, provides less stress and more resistance to failure by breakage of relaxation. Finally, the design of the self-locking plug 10 of the invention is far more compact than conventional plug designs.

It will be appreciated that the self-locking plug 10 of the invention can be used for other applications other than borescope plugs. For example, the self-locking plug 10 can be used various separable connectors, such as those used in electrical, fluid, hydraulic, and pneumatic lines, mechanical fasteners, such as nuts and bolts, and adjustable linkages in which a jam nut must be prevented from loosening. The self-locking plug 10 of the invention can also be used as a torque limiting device or clutch in a power train.

The patents and other documents identified herein are hereby incorporated by reference herein. Other embodiments of the invention will be apparent to those skilled in the art from a consideration of the specification or a practice of the invention disclosed herein. It is intended that the specification and examples are illustrative only and are not intended to be limiting on the scope of the invention. The true scope and spirit of the invention is indicated by the following claims. 

What is claimed is:
 1. A self-locking plug, comprising: a body component; a flexible beam finger component disposed about the body component and including a plurality of axially-oriented flexible beam fingers; a tab sleeve component disposed within the flexible beam finger component and including one or more downward extending tabs; an annular detent ring component including a plurality of circumferentially-arranged detents separated by ridges in radial alignment with the plurality of flexible beam fingers; and a wave spring disposed between the tab sleeve component and the annular detent ring component for providing a biasing force to urge the tab sleeve component in a direction of a central, longitudinal axis, A, of the self-locking plug, wherein the plurality of flexible beam fingers travel across the plurality of detents to cause elastic deformation of the flexible beam fingers when the body component is rotated about the central, longitudinal axis, A, of the self-locking plug.
 2. The self-locking plug according to claim 1, wherein the number of detents is equal to the number of flexible beam fingers.
 3. The self-locking plug according to claim 1, wherein the body component includes a flange, and wherein the flexible beam finger component includes a flange radially inward from the flexible fingers, and wherein the flange of the body component and the flange of the flexible beam finger component engage each other when the self-locking plug is assembled.
 4. The self-locking plug according to claim 3, wherein the flange of the flexible beam finger component includes one or more slots adapted to receive the one or more tabs of the tab sleeve component.
 5. The self-locking plug according to claim 4, wherein the one or more slots prevent rotation between of the tab sleeve component and the flexible beam finger component when the one or more tabs are received by the one or more slots, thereby providing an anti-rotation feature between the flexible beam finger component and the tab sleeve component of the self-locking plug.
 6. The self-locking plug according to claim 4, wherein the flexible beam finger component includes two slots that are spaced 180 degrees apart from each other, and wherein the tab sleeve component includes two tabs that are spaced 180 degrees apart from each other.
 7. The self-locking plug according to claim 1, wherein the one or more tabs engage a slot formed in a borescope port and prevent rotation of the self-locking plug when the body component about the central, longitudinal axis of the self-locking plug, thereby providing an anti-rotation feature between the tab sleeve component and the borescope port.
 8. The self-locking plug according to claim 1, wherein the detents are always engaged with the flexible beam fingers when the flexible beam finger component is rotated relative to the annular detent ring component.
 9. The self-locking plug according to claim 1, wherein each detent has a generally concave surface and is separated by a substantially planar surface for facilitating interaction with the flexible beam fingers as the plurality of flexible beam fingers travel across the plurality of detents.
 10. A self-locking plug, comprising: a body component; a flexible beam finger component disposed about the body component and including a plurality of axially-oriented flexible beam fingers; a tab sleeve component disposed within the flexible beam finger component and including one or more downward extending tabs; an annular detent ring component including a plurality of circumferentially-arranged detents separated by ridges in radial alignment with the plurality of flexible beam fingers; and a wave spring disposed between the tab sleeve component and the annular detent ring component for providing a biasing force to urge the tab sleeve component in a direction of a central, longitudinal axis, A, of the self-locking plug, wherein the flexible beam finger component moves relative to the annular detent ring component when the body component is rotated about the central, longitudinal axis, A, of the self-locking plug, thereby causing the plurality of flexible beam fingers to travel across the plurality of detents and cause elastic deformation of the flexible beam fingers.
 11. The self-locking plug according to claim 10, wherein the number of detents is equal to the number of flexible beam fingers.
 12. The self-locking plug according to claim 10, wherein the body component includes a flange, and wherein the flexible beam finger component includes a flange radially inward from the flexible fingers, and wherein the flange of the body component and the flange of the flexible beam finger component engage each other when the self-locking plug is assembled.
 13. The self-locking plug according to claim 12, wherein the flange of the flexible beam finger component includes one or more slots adapted to receive the one or more tabs of the tab sleeve component.
 14. The self-locking plug according to claim 13, wherein the one or more slots prevent rotation between of the tab sleeve component and the flexible beam finger component when the one or more tabs are received by the one or more slots, thereby providing an anti-rotation feature between the flexible beam finger component and the tab sleeve component of the self-locking plug.
 15. The self-locking plug according to claim 13, wherein the flexible beam finger component includes two slots that are spaced 180 degrees apart from each other, and wherein the tab sleeve component includes two tabs that are spaced 180 degrees apart from each other.
 16. The self-locking plug according to claim 10, wherein the one or more tabs engage a slot formed in a borescope port and prevent rotation of the self-locking plug when the body component about the central, longitudinal axis of the self-locking plug, thereby providing an anti-rotation feature between the tab sleeve component and the borescope port.
 17. The self-locking plug according to claim 10, wherein the detents are always engaged with the flexible beam fingers when the flexible beam finger component is rotated relative to the annular detent ring component.
 18. The self-locking plug according to claim 10, wherein each detent has a generally concave surface and is separated by a substantially planar surface for facilitating interaction with the flexible beam fingers as the plurality of flexible beam fingers travel across the plurality of detents. 